Apparent ABS coming in at low speeds. Why

I am trying to diagnose a problem on my mates a4 2.8 quattro. When he is at very low speeds or slowing down and applying the brake, the ABS seems to operate when there is no loss of grip. It only seems to do it on the front. When I looked at the output for the wheel speed sensors, the front pair seemed to from to zero before the rears did. My suspicion is it's seeing the speed differential and kicking in. However there are no codes for the sensors or anything else. Is this a common problem? Any other suggestions appreciated as I don't want to start swapping bits due to the low value of the car.

Cheers Mike


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This can be a common issue. Mine does it also I think one of my rear ABS rings is the problem but as yet have not confirmed this. My ABS sensors are fine so I have just disconected it by unplugging one ABS sensor and the fault of the ABS kicking in at slow speeds has stopped.
As far as I am aware this will actually turn the ABS system off which I know isn't a good thing so I must pull my finger out and get it sorted.

Let us know how you get on with it.

Yes it is a common problem, the teeth on the cv joint get corroded and dirty and/or the sensors get old and lose the signal just as you come down to about 5mph and then the ABS thinks the wheels are locked so tries to unlock them, which can be a trouser soiling experience. We have this on a 2011 Toureq last week which was down to both right hand side wheel bearings having corroded sender rings but your friends does not use that system. On the Touareg the parts are genuine only and the job costs £600 a corner.

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Originally Posted by Crasher

Yes it is a common problem, the teeth on the cv joint get corroded and dirty and/or the sensors get old and lose the signal just as you come down to about 5mph and then the ABS thinks the wheels are locked so tries to unlock them, which can be a trouser soiling experience. We have this on a 2011 Toureq last week which was down to both right hand side wheel bearings having corroded sender rings but your friends does not use that system. On the Touareg the parts are genuine only and the job costs £600 a corner.

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Thanks for that. It seems I was right in my suspicion then. I will check the speed rings first ad the car does have a lot of corrosion on the underneath. Are these available separately or is it a new cv joint?

Cheers


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I had the same after installing new bearings on the back of a non 4wheel drive car. I cleaned the abs rings while doing that.
While still on the car, I could spin the wheel to confirm the ring had a wobble.
With a long screwdriver I could bent it a bit and it never was an issue again.
Those rings are availlable and cheap. Under 10 euro a piece. Dont know about the 4wheel drive versions though.